<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <!--<link rel="stylesheet" href="a.css">-->
    <style>
        @import "a.css";/*这种方法也是相当于引用外部样式*/
    </style>
</head>
<body>
<div>hello css</div>
<div>hello css</div>
</body>
</html>